Hi & thanks again for taking the time to help

OK logs below from each office (I have removed IP from the end for security):

Head Office

"2013-10-03 09:26:33", "Initiating IKE Main Mode to "

"2013-10-03 09:27:04", "Responding to Main Mode from "

"2013-10-03 09:27:13", "Initiating IKE Main Mode to "

"2013-10-03 09:27:29", "Responding to Main Mode from "

"2013-10-03 09:27:33", "Initiating IKE Main Mode to "

"2013-10-03 09:28:13", "Initiating IKE Main Mode to "

"2013-10-03 09:28:33", "Initiating IKE Main Mode to "

"2013-10-03 09:28:54", "Initiating IKE Main Mode to "

"2013-10-03 09:29:43", "Initiating IKE Main Mode to "

"2013-10-03 09:30:04", "Initiating IKE Main Mode to "

"2013-10-03 09:30:43", "Initiating IKE Main Mode to "

"2013-10-03 09:31:04", "Initiating IKE Main Mode to "

"2013-10-03 09:31:43", "Initiating IKE Main Mode to "

"2013-10-03 09:32:04", "Initiating IKE Main Mode to "

"2013-10-03 09:32:43", "Initiating IKE Main Mode to "

"2013-10-03 09:33:04", "Initiating IKE Main Mode to "

Remote Office:

"2013-10-03 09:27:11", "Re-dial L2L[1], ifno: 12, status: 0 from WEB..."

"2013-10-03 09:27:11", "DropVPN() VPN : Dial-out Profile Index = 1, Name = Staines"

"2013-10-03 09:27:11", "Initiating IKE Main Mode to "

"2013-10-03 09:27:35", "Initiating IKE Main Mode to "

"2013-10-03 09:34:46", "Initiating IKE Main Mode to "

"2013-10-03 09:35:30", "Re-dial L2L[1], ifno: 12, status: 0 from WEB..."

"2013-10-03 09:35:30", "DropVPN() VPN : Dial-out Profile Index = 1, Name = Staines"

"2013-10-03 09:35:30", "Initiating IKE Main Mode to "

There are plenty of initiations but not many responses! Where you've removed the IP address at the end of the two responses from the Head Office log, are they the correct IP address for the remote site? If not, then you've got a problem with the IP addresses at one or both of the sites not being the same as when the tunnel was first created.

If it is the correct IP address, check on the WAN status page of the remote site that the WAN IP is still the same as you thought.